In recent years, discrete paper feeders are used in facsimiles, printers, copying machines, etc., for discretely transferring two or more sheets of manuscript or copying paper one by one. In such a discrete paper feeder, it is necessary to detect the rear end of a manuscript with a sensor or the like disposed in the device in order to detect the completion of transfer of a sheet of the manuscript. For this purpose, it is necessary that the device be able to perceive that reading of a sheet of the manuscript has been completed. It is thus necessary to put intervals between successive sheets of a manuscript that are fed in sequence. In order to put intervals between successive sheets, various configurations can be employed such as to forcibly create feeding intervals by using a reverse roller, an electromagnetic clutch or a solenoid. Especially in the type of discrete paper feeders that have been developed in a large number, manuscript intervals are produced by creating a difference between the peripheral speeds of the rotation of a transfer roller and a separation roller and rotating the transfer roller at a speed 10% to 30% higher than that of the separation roller.
FIG. 14 is a perspective view of an essential part of an example of a conventional discrete paper feeder. Conventional discrete paper feeder 61 includes separation roller 62, transfer roller 63, separation plate 64, separation roller gear 65, delay member 66, one-way clutch spring 67, transfer roller gear 68, reader 69, and butting member 69A.
A description of the action of conventional discrete paper feeder 61 as configured above will be given with reference to the illustration.
Separation roller gear 65 and rotation shaft 62A transmit the power of a drive motor (not shown) to separation roller 62. Separation roller 62 is rotated by this power and transfers manuscript 80 toward reader 69 and transfer roller 63. During this process, manuscript 80 is discretely fed page by page by separation plate 64 that is disposed in a manner pressed to separation roller 62.
Transfer roller gear 68 and rotation shaft 63B transmit the power of a drive motor (not shown) to transfer roller 63. Transfer roller 63 is rotated by this power. Here, the device is so structured that transfer roller 63 is rotated at a peripheral speed that is 10% to 30% higher than that of separation roller 62. Such a structure is realized by selecting gear ratios of two or more transmission gears (not shown) that transmit the power of the drive motor. This difference in the peripheral speeds generates a time difference between the time when manuscript 80 is bitten and transferred by transfer roller 63 and the time when the next sheet of manuscript is bitten by separation roller 62 and transferred to and bitten by transfer roller 63. This time difference creates an interval between two consecutively transferred manuscript sheets.
One-way clutch spring 67 is provided in the part where rotation shaft 62A of separation roller 62 and separation roller gear 65 are coupled for absorbing the peripheral speed difference between separation roller 62 and transfer roller 63. Furthermore, delay member 66 is provided in the part where rotation shaft 62A of separation roller 62 and separation roller gear 65 are coupled. That is, rotation shaft 62A and separation roller gear 65 are coupled with play. Because of this structure, the timing of biting a manuscript by separation roller 63 is delayed thus causing a further increase in the interval of manuscript sheets.
In such discrete paper feeder 61, a single transfer roller 63 is disposed, and reader 69 is disposed between separation roller 62 and transfer roller 63. This is for the sake of reduction in size and manufacturing cost. With this structure, before manuscript 80 that is bitten by separation roller 62 and transferred is bitten by transfer roller 63, reading of manuscript 80 by reader 69 is started. When manuscript 80 is bitten by transfer roller 63, manuscript 80 is transferred from that position at the peripheral speed of transfer roller 63. Consequently, the transfer speed of manuscript 80 changes due to a difference between the peripheral speeds of separation roller 62 and transfer roller 63. Accordingly, distortion and elongation of the image read from manuscript 80 by reader 69 is caused at the position where the transfer speed changes. In order to cope with this situation, in discrete paper feeder 61, the peripheral speed difference between separation roller 62 and transfer roller 63 is made to be as small as possible to minimize the distortion and elongation of read images so that the distortion will not be prominent. Furthermore, with a view to minimizing the distortion and elongation of the read images due to peripheral speed difference between separation roller 62 and transfer roller 63, transfer roller 63 is disposed as close to reader 69 as possible in a manner pressed against butting member 69A.
Also, another example of a conventional discrete paper feeder as disclosed in Japanese Patent Laid-Open Application No. H6-263273 includes a sun gear, a planetary arm and a planetary gear, a planetary gear shaft, and a pressing spring. The device also includes a fixed-disc cam mechanism for absorbing pressing force of the pressing spring via the planetary gear and at the same time allowing rotation and revolution of the planetary gear.
However, the conventional discrete paper feeders as described above suffer from the following problems.
(1) Even when transfer roller 63 is disposed close to reader 69 as described above, distortion and elongation of read images occur at the front end of manuscript 80, making the transmitted manuscript hard to read or spoiling the appearance.
(2) There is a limit in setting the peripheral speed difference as a sufficient interval between manuscript sheets cannot be obtained when the peripheral speed difference is made too small. If a sufficient manuscript interval is to be obtained, occurrence of distortion and elongation of the read image of a manuscript is unavoidable.
(3) If the reader is of high performance, it is possible to read a manuscript at a high speed by increasing the speed of transfer. Here, the peripheral speed difference has to be small as entry of a manuscript under transfer roller 63 cannot be smoothly performed. However, when the peripheral speed difference is made too small, a predetermined manuscript interval cannot be obtained.